Foodstuffs packaging containing a film with properties providing a barrier to mineral oils

ABSTRACT

The present invention relates to foodstuffs packaging containing a polyolefin-based film with properties providing a barrier to mineral oils.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application (under U.S.C. §371) of PCT/EP2013/003369, filed Nov. 8, 2013, which claims benefit of European Application No. 12 007 669.0, filed Nov. 12, 2012, both of which are incorporated herein by reference in their entirety.

The present invention relates to a foodstuffs packaging containing a polyolefin-based film with properties providing a barrier to mineral oils.

Polyolefin-based films, in particular biaxially oriented propylene (boPP) films, are nowadays used as packaging films in a wide range of applications. Polypropylene films are characterised by many advantageous use properties, such as high transparency, gloss, barrier to water vapour, good printability, rigidity, penetration strength, etc. The polypropylene films can be used both as transparent films and as opaque films.

The above films are often also used in combination with other packaging materials, in particular in the field of foodstuffs.

For foodstuffs packaging, cardboard packaging is often used that, due to its availability, is often present in the form of recycled cardboard. This results in problems, since recycled cardboards typically contain 300-1000 mg/kg mineral oil with a relatively low molar mass (primarily n-C18 to n-C22) and a content of aromatic components between 15-20% (opinion no. 008/2010 of the Federal Institute for Risk Assessment “BfR” of Sep. 12, 2009).

The mineral oil mixtures detected in recycled cardboard are paraffin-like (open-chained, usually branched) and naphthene-like (cyclical) hydrocarbons that are referred to as “mineral oil saturated hydrocarbons” (MOSH), and also aromatic hydrocarbons, or “mineral oil aromatic hydrocarbons” (MOAH), which consist primarily of highly alkylated systems (see Biedermann M, Fiselier K, Grob K, 2009, “Aromatic hydrocarbons of mineral oil origin in foods: Method for determining the total concentration and first results. Journal of Agricultural and Food Chemistry 57: 8711-8721).

Insofar as no suitable precautionary measures are taken, for example by metallisation of the cardboard, there is thus the risk that the above-specified mineral oil mixtures will contaminate the foodstuffs to be packaged or already packaged.

First approaches for using films based on polyolefin films, in particular biaxially oriented polypropylene (boPP) films, as barrier to the above-specified mineral oil mixtures show that the polyolefin films alone do not effectively prevent the migration. The films thus require an additional finishing in order to act as a barrier to the above-specified mineral oil mixtures.

By way of example, films that have a metallisation with sufficient optical density are suitable. This metal layer forms an effective barrier against the mineral oils. For some applications, however, such metal layers are undesirable for aesthetic reasons or for cost reasons. In particular, these metal layers cannot be used when the film packaging is to be transparent. Furthermore, the efficacy as a barrier is also dependent on the quality of the coating, such that only a high-quality costly metallisation serves this purpose.

The object of the present invention was to provide a polyolefin-based film, in particular a film based on biaxially oriented polypropylene (boPP) films, for foodstuffs packaging formed from recycled cardboard, which film has a sufficient barrier to mineral oil mixtures and at the same time retains the good application properties, such that a contamination of the foodstuff to be packaged or already packaged by the mineral oil mixture in the recycled cardboard is avoided.

The present invention thus relates to a foodstuffs packaging comprising:

-   a) a foodstuff, -   b) a polyolefin-based film, in particular a film based on biaxially     oriented polypropylene (boPP) films, which film encases the     foodstuff, -   c) a cardboard based on recycled cardboard, which encases the     polyolefin-based film, in particular the film based on biaxially     oriented polypropylene (boPP) films, containing the foodstuff,     -   characterised in that the polyolefin-based film, in particular         the film based on biaxially oriented polypropylene (boPP) films,         comprises at least one coating comprising (i) acrylate polymer         and/or (ii) halogen-containing vinyl polymers and/or vinylidene         polymers and/or (iii) polymers based on vinyl alcohol (VOH), and         this coating is present on the side of the film facing towards         the cardboard based on recycled cardboard.

The foodstuffs packaging according to the invention does not require any barrier layers produced by metallisation of surfaces and can thus be produced more economically than a metallised cardboard or a metallised film, for example. In addition, with use of transparent embodiments, the invention enables new types of packaging that previously were not possible on account of the metallisation.

A BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 illustrates a test structure containing cardboard saturated with a defined quantity of mineral oil which was covered with the sample to be measured, Tenax® was distributed thereon.

The invention can be provided by differently designed foodstuffs packagings. In one embodiment bag packaging or wrap packaging is produced with technology known per se and contains the foodstuff. The filled bag or wrap packaging is then packaged in a further encasing cardboard packaging. The coating on the outer side of the bag or wrap packaging prevents the migration of the mineral oils from the cardboard into the foodstuff. In a further embodiment the cardboard can be laminated or lined with the coated film. A packaging that contains the foodstuff is then produced from the coated cardboard. This variant is advantageous for packaging in which the foodstuff would otherwise come into direct contact with the cardboard.

Film

The polyolefin-based films used within the scope of the present invention are in particular films based on biaxially oriented polypropylene (boPP) films. These films can be constructed in a monolayer or multi-layer manner and have a coating comprising (i) acrylate polymer and/or (ii) halogen-containing vinyl polymers and/or vinylidene polymers and/or (iii) polymers based on vinyl alcohol (VOH).

The monolayer film or the base layer of the multilayer film contains polyolefin, preferably a propylene polymer and optionally further conventional additives in effective quantities in each case. The base layer generally contains at least 70 to <100% by weight, preferably 75 to 98% by weight, in particular 85 to 95% by weight, of the polyolefin, in each case in relation to the weight of the layer.

Propylene polymers are preferred as polyolefins of the base layer or as material for monolayer films. These propylene polymers contain 90 to 100% by weight, preferably 95 to 100% by weight, in particular 98 to 100% by weight, of propylene units and have a melting point of 120° C. or above, preferably 150 to 170° C., and generally a melt flow index from 1 to 10 g/10 min, preferably 2 to 8 g/10 min, at 230° C. and a force of 21.6 N (DIN 53735). Isotactic propylene homopolymer with an atactic proportion of 15% by weight and below, copolymers of ethylene and propylene with an ethylene content of 5% by weight or below, copolymers of propylene with C₄-C₈ olefins with an olefin content of 5% by weight or below, and terpolymers of propylene, ethylene and butylene with an ethylene content of 10% by weight or below and with a butylene content of 15% by weight or below are preferred propylene polymers for the base layer, wherein isotactic propylene homopolymer is particularly preferred. The specified percentages by weight relate in each case to the respective polymers.

Furthermore, a mixture of the specified propylene homopolymers and/or copolymers and/or terpolymers and other polyolefins, in particular of monomers with 2 to 6 C atoms, is suitable, wherein the mixture contains at least 50% by weight, in particular at least 75% by weight, of propylene polymer. Suitable other polyolefins in the polymer mixture are polyethylenes, in particular HDPE, MDPE, LDPE, VLDPE and LLDPE, wherein the proportion of each of these polyolefins does not exceed 15% by weight in relation to the polymer mixture.

In an opaque embodiment the base layer of the film or the monolayer film contains vacuole-initiating fillers in a quantity of at most 30% by weight, preferably 5 to 25% by weight, in relation to the weight of the opaque base layer.

Vacuole-initiating fillers are solid particles that are incompatible with the polymer matrix and, as the films are stretched, lead to the formation of vacuole-like cavities. The vacuole-initiating fillers generally have a minimum size of 1 μm in order to lead to an effective, i.e. opaque-making, quantity of vacuoles. The mean particle diameter of the particles is generally 1 to 6 μm, preferably 1.5 to 5 μm. The chemical nature of the particles plays a subordinate role.

Conventional vacuole-initiating fillers are inorganic and/or organic materials incompatible with polypropylene, such as aluminium oxide, aluminium sulphate, barium sulphate, calcium carbonate, magnesium carbonate, silicates such as aluminium silicate (kaolin clay) and magnesium silicate (talc) and silicon dioxide, from which calcium carbonate and silicon dioxide are preferably used. The conventionally used polymers incompatible with the polymers of the base layer are considered as organic fillers, in particular copolymers of cyclic olefins (COC) as described in EP-A-O 623 463, polyesters, polystyrenes, polyamides, halogenated organic polymers, wherein polyesters such as polybutylene terephthalates and cycloolefin copolymers are preferred. Incompatible materials or incompatible polymers in the sense of the present invention means that the material or the polymer is present in the film in the form of separate particles or in the form of a separate phase.

In a further opaque embodiment the base layer or the monolayer films, additionally or alternatively to the vacuole-initiating fillers, contain pigments, for example in a quantity from 0.5 to 10% by weight, preferably 1 to 8% by weight, in particular 1 to 5% by weight. The specified quantities relate to the weight of the layer.

Pigments in the sense of the present invention are incompatible particles that essentially do not lead to vacuole formation as the film is stretched. The, for example, colouring effect of the pigments is caused by the particles themselves. Pigments are both what are known as “white pigments” which colour the films white, and “coloured pigments” which provide the film with a bright or black colour. Generally the mean particle diameter of the pigments lies in the range from 0.01 to 1 μm, preferably 0.01 to 0.7 μm, in particular 0.01 to 0.4 μm.

Conventional pigments are materials such as aluminium oxide, aluminium sulphate, barium sulphate, calcium carbonate, magnesium carbonate, silicates such as aluminium silicate (kaolin clay) and magnesium silicate (talc), silicon dioxide and titanium dioxide, from which white pigments such as calcium carbonate, silicon dioxide, titanium dioxide and barium sulphate are preferably used. Titanium dioxide is particularly preferred. Various modifications and coatings of TiO₂ are known per se in the prior art.

The density of the film is determined essentially by the density of the base layer. The density of the base layer generally lies in a range from 0.45-0.95 g/cm³. The vacuoles reduce the density of the base layer, and pigments increase the density of the base layer compared with the density of polypropylene (˜0.9 g/cm³).

The thickness of the film lies generally in a range from 20 to 100 μm, preferably 25 to 60 μm, in particular 30 to 50 μm. Insofar as the films have a multi-layered structure, the thickness of the base layer is between 10 and 60 μm, preferably between 10 and 40 μm. The above-mentioned thicknesses are to be understood without the coating comprising (i) acrylate polymer and/or (ii) halogen-containing vinyl and/or vinylidene polymers and/or (iii) polymers based on vinyl alcohol (VOH).

Insofar as the film is multi-layered, the films also comprise, besides the specified base layer, further layers that are applied at least to one side or to both opposite sides of the base layer. A three-layered structure of the film thus results in the case of two cover layers.

The thickness of the cover layer is generally 0.5-3 μm. In a further embodiment of the invention intermediate layers are also located on one or both sides between the cover layer and the base layer, the thickness of said intermediate layers lying in the range from 1 to 8 μm. With a combination of intermediate layer and cover layer, these together preferably have a total thickness from 2 to 8 μm.

The cover layers can be formed as a sealable layer, wherein this is understood to mean both heat-sealable and cold-sealable layers. Cold seal coatings can be applied directly to the surface of a monolayer film. However, it is generally preferred to cover the base layer first with a coextruded polymer layer and to apply the cold seal coating to this polymer cover layer. Suitable materials for the hot-sealable cover layer are the homopolymers, copolymers and terpolymers specified hereinafter.

To improve the adhesion, the surface of the film is subjected, prior to the coating in a manner known per se by means of corona, flame or plasma, to a method in order to increase the surface tension. The surface tension of the layer thus treated then lies typically in a range from 35 to 45 mN/m. This surface treatment can be performed on one or both surfaces of the film.

The above-described cover and intermediate layer generally contain at least 80% by weight, preferably 90 to <100% by weight of olefin polymers or mixtures thereof, and optionally also conventional additives, in each case in effective quantities. Suitable polyolefins are, for example, polyethylenes, propylene copolymers and/or propylene terpolymers, and also the propylene homopolymers already described in conjunction with the base layer.

Suitable propylene copolymers or terpolymers are generally constructed from at least 50% by weight of propylene units and ethylene units and/or butylene units as comonomer. Preferred mixed polymers are static ethylene-propylene copolymers with an ethylene content from 2 to 10% by weight, preferably 5 to 8% by weight, or static propylene-butylene-1 copolymers with a butylene content from 4 to 25% by weight, preferably 10 to 20% by weight, in each case in relation to the total weight of the copolymer, or static ethylene-propylene-butylene-1 terpolymers with an ethylene content from 1 to 10% by weight, preferably 2 to 6% by weight, and a butylene-1 content from 3 to 20% by weight, preferably 8 to 10% by weight, in each case in relation to the total weight of the terpolymer. These co- and terpolymers generally have a melt flow index from 3 to 15 g/10 min, preferably 3 to 9 g/10 min (230° C., 21.6 N DIN 53735) and a melting point from 70 to 145° C., preferably 90 to 140° C. (DSC).

Suitable polyethylenes are, for example, HDPE, MDPE, LDPE, LLDPE and VLDPE, from which HDPE and MDPE types are particularly preferred. The HDPE generally has an MFI (50 N/190° C.) of greater than 0.1 to 50 g/10 min, preferably 0.6 to 20 g/10 min, measured in accordance with DIN 53 735, and a viscosity number, measured in accordance with DIN 53 728, part 4, or ISO 1191, in the range from 100 to 450 cm³/g, preferably 120 to 280 cm³/g. The crystallinity is 35 to 80%, preferably 50 to 80%. The density, measured at 23° C. in accordance with DIN 53 479, method A, or ISO 1183, lies in the range from >0.94 to 0.96 g/cm³. The melting point, measured with DSC (maximum of the melt curve, heating rate 20° C./min), lies between 120 and 140° C. Suitable MDPE generally has an MFI (50 N/190° C.) of greater than 0.1 to 50 g/10 min, preferably 0.6 to 20 g/10 min, measured in accordance with DIN 53 735. The density, measured at 23° C. in accordance with DIN 53 479, method A, or ISO 1183, lies in the range from >0.925 to 0.94 g/cm³. The melting point, measured with DSC (maximum of the melt curve, heating rate 20° C./min), lies between 115 and 130° C.

The film generally contains, in the respective layers, conventional stabilisers and neutralising agents in conventional quantities, and optionally antiblocking agents in the cover layer(s). Only additives or quantities of additives that do not impair the coatings are added as lubricants and antistatic agents to the layers.

The conventional compounds having a stabilising effect for ethylene, propylene and other olefin polymers can be used as stabilisers. The added quantity of said compounds lies between 0.05 and 2% by weight. Phenolic stabilisers, alkali/alkaline earth stearates and/or alkali/alkaline earth carbonates are particularly suitable. Phenolic stabilisers are preferred in a quantity from 0.1 to 0.6% by weight, in particular 0.15 to 0.3% by weight, and with a molar mass of more than 500 g/mol. Pentaerythrityl tetrakis-3-(3,5-di-tertiary butyl-4-hydroxyphenyl)propionate or 1,3,5-trimethyl-2,4,6-tris(3,5-di-tertiary butyl-4-hydroxybenzyl)benzene are particularly advantageous.

Neutralising agents are preferably calcium carbonate and/or dihydrotalcite (DHT) of a mean particle size of at most 0.7 μm, an absolute particle size of less than 10 μm, and a specific surface area of at least 40 m²/g. Neutralising agents in a quantity from 50 to 1000 ppm, in relation to the layer, are generally used.

Suitable antiblocking agents are inorganic additives such as silicon dioxide, calcium carbonate, magnesium silicate, aluminium silicate, calcium phosphate and the like and/or incompatible polymers, such as polymethyl methacrylate (PMMA) polyamides, polyesters, polycarbonates and the like, preferably polymethyl methacrylate (PMMA), silicon dioxide and calcium carbonate. The effective quantity of antiblocking agent lies in the range from 0.1 to 2% by weight, preferably 0.1 to 0.5% by weight, in relation to the respective cover layer. The mean particle size lies between 1 and 6 μm, in particular 2 and 5 μm, wherein particles with a spherical form, as described in EP-A-0 236 945 and DE-A-38 01 535, are particularly suitable.

The film provided in the packaging according to the invention is produced by means of processes and methods known per se.

In respect of the subsequent coating, the film should generally have no migrating additives in any layer, for example should comprise no lubricants or antistatic agents, since these may lead to problems with regard to the adhesion of the coating.

Coating

The polyolefin-based films used within the scope of the present invention, in particular the films based on biaxially oriented polypropylene (boPP) films, have a coating comprising (i) acrylate polymer and/or (ii) halogen-containing vinyl and/or vinylidene polymers and/or (iii) polymers based on vinyl alcohol (VOH). The coating may be present on one or both sides of the film.

The total thickness of the coating per side of the film is generally between 0.1-5 μm, preferably between 0.5-3 μm. The coating may be applied in a multiple layers, wherein combinations of different materials/polymers, for example acrylate polymer and polyvinylidene dichloride (PVDC), are also used. In the present case, multiple layers means that, per layer, one of the specified materials selected from the group acrylate polymer, polyvinylidene dichloride (PVDC) or polymers based on vinyl alcohol (VOH) is present as primary component.

The film is generally treated initially on the side to be coated so as to increase the surface tension. Once the surface tension has been increased, an adhesion promoter is usually applied to the surface to be coated. Such adhesion promoters are known per se and are based for example on polyurethane, acrylate polymers or polyethylene imines. The adhesion promoters can also be applied in multiple layers (secondary adhesion promoter layer), wherein combinations of different adhesion promoters are also possible. In the present case, multiple layers means that, per layer, one of the above-mentioned adhesion promoters is present as primary component. If aqueous polyethylene imine solution is applied as adhesion promoter, this usually contains 1% by weight of polyethylene imine. Polyethylene imine solution promotes the subsequent coating, as described in EP-A-0255870.

The coating materials according to the invention are (i) acrylate polymer and/or (ii) halogen-containing vinyl polymers and/or vinylidene polymers and/or (iii) polymers based on vinyl alcohol (VOH). These are in each case arranged as a specific layer. Specific layers are homogeneous layers made of a defined coating material. Here, mixtures of the above-specified materials/polymers are not desirable for the respective coating material, but are not ruled out in the form of copolymers.

Besides the above-specified materials, the coatings possibly also contain further components, for example as lubricants, preferably non-migrating lubricants, such as waxes and/or antiblocking agents.

The coating materials according to the invention are applied as dispersions, in particular aqueous dispersions, of which the solids content is between 10 to 70% by weight, preferably 20-60% by weight.

The acrylate polymers used in accordance with the invention are preferably acrylate homopolymers and/or acrylate copolymers based on, for example, alkyl acrylates, such as methyl methacrylate and/or ethyl acrylate, or further comonomers, such as unsaturated carboxylic acids or substituted vinyl compounds. An acrylate copolymer can be constructed from 2 or more different monomers. Furthermore, mixtures of the respective acrylate homopolymers and/or acrylate copolymers are possible. Materials of this type are obtainable on the market for example under the name NeoCryl BT-36 and NeoCryl FL-711 from the company DSM NeoResins (Netherlands) or under another name from the company BASF. Preferred aqueous coating dispersions based on acrylate polymer comprise at least 80% by weight acrylate dispersion, at least 10% by weight wax dispersion, at least 12% by weight dispersion of a colloidal silica, and at least 7% by weight of antiblocking agent dispersion. The differences to make up 100% by weight consist of water. The quantity of acrylate coating per side of the film after drying is generally between 0.1 and 1.5 g/m². The thickness of this acrylate layer is <2.0 μm, inclusive of the layer of the adhesion promoter.

The halogen-containing vinyl polymers and/or vinylidene polymers used in accordance with the invention are preferably polymers based on vinyl chloride homopolymers and/or vinylidene chloride homopolymers and/or copolymers, wherein the comonomer originates from the group of vinyl acetates, vinyl halides or acrylates. The individual monomers can be present in different weighting in the copolymer. Such materials are obtainable on the market for example under the name Diofan® A 297, Diofan® A 114 and Diofan® B 200 from the company SolVin.S.A. (Belgium). Preferred aqueous coating dispersions based on halogen-containing vinyl polymers and/or vinylidene polymers, in particular polyvinylidene dichloride (PVDC), comprise at least 95% by weight of PVDC acrylate copolymer dispersion, at least 10% by weight of wax dispersion, at least 7% by weight of antiblock dispersion. The differences to make up 100% by weight consist of water. The quantity of coating per side of the film after drying is generally between 2.5 and 4 g/m². The thickness of this layer is <4.5 μm, inclusive of the layer of the adhesion promoter.

The polymers based on vinyl alcohol (VOH) used in accordance with the invention are vinyl polymers that are known per se. Preferred aqueous coating materials based on vinyl alcohol (VOH) are ethylene vinyl alcohol (EVOH) and comprise 5-15% by weight of a mixture of ethylene vinyl alcohol and polyvinyl alcohol, preferably in the ratio 0.8-1.2 to 1.2-0.8, in particular 1:1 ratios by weight. The quantity of coating per side of the film after drying is generally between 0.5 and 1.0 g/m² for coating materials based on vinyl alcohol (VOH). The thickness of this layer is <2.0 μm, inclusive of the layer of the adhesion promoter.

The coating materials according to the invention are applied preferably after the increase of the surface tension, for example by corona treatment, whereby the adhesion is improved. As already mentioned, an adhesion promoter is usually applied to the side to be coated following the surface treatment and is dried. Insofar as a secondary adhesion promoter (second adhesion promoter layer) is advantageous, this is also applied. The adhesion promoter and the coating materials are applied in accordance with methods known per se, such as roller coating (roll application systems, for example with engraved rolls), curtain coating, spray coating. The applied coating is then dried using conventional drying methods (for example hot air).

The coated films are used in accordance with the invention such that the coated side of the film faces towards the loaded cardboard. Surprisingly, the coating in direct contact with the loaded cardboard constitutes an effective migration barrier. Thus, the alternative metallisation of the film or of the cardboard can be omitted. The packaging according to the invention is therefore preferably free from an additional metal layer. This, however, does not rule out metallic prints or similar metallic decorations. Cost-efficient packaging made of loaded cardboard packaging can thus be produced, with which no considerable quantities or even no quantity of mineral oils migrate into the foodstuff.

DEFINITION OF RECYCLED CARDBOARD

The cardboard based on recycled cardboard used within the scope of the present invention is constituted by cardboard packaging that comprises significant quantities of mineral oils and is thus subject to the provisions of COMMISSION REGULATION (EC) no. 1935/2004 of 27 Oct. 2004 (also referred to hereinafter or below as loaded cardboard packaging).

Cardboard packaging of this type based on recycled cardboard typically contains at least 300-1000 mg/kg mineral oil. These mineral oils are referred to as “mineral oil saturated hydrocarbons” (MOSH) or as “mineral oil aromatic hydrocarbons” (MOAH). The MOSH and MOAH mineral oils are often also specified in terms of their carbon chains, for example as MOSH 14-24, MOSH 24-35, MOAH 14-24 and MOAH 24-35, wherein the numerical value reflects the number of carbon atoms. The exact composition of the MOSH and MOAH mineral oils is dependent on the type of recycled cardboard, i.e. the fractions of MOSH 14-24, MOSH 24-35, MOAH 14-24 and MOAH 24-35 are different.

The film provided in the foodstuffs packaging according to the invention has good barrier properties with respect to MOSH and MOAH mineral oils, in particular with respect to MOSH 14-24, MOSH 24-35, MOAH 14-24 and MOAH 24-35.

The film provided in the foodstuffs packaging according to the invention preferably has a good barrier to MOSH and MOAH mineral oils, such that it may come into contact with foodstuffs in accordance with COMMISSION REGULATION (EC) no. 1935/2004 of 27 Oct. 2004. A foodstuff simulant, i.e. a test medium, that mimics dry foodstuffs pursuant to COMMISSION REGULATION (EC) no. 10/2011 of 14 Jan. 2011 is understood to be a foodstuff. The behaviour of this foodstuff simulant mimics the migration from foodstuff contact materials.

With the use according to the invention of the coated film in the foodstuffs packaging according to the invention, merely at most 1%, in particular at most 0.5%, of the MOSH 14-24 fraction present in the recycled cardboard preferably migrates into a foodstuff simulant pursuant to COMMISSION REGULATION (EC) no. 10/2011 of 14 Jan. 2011 (Tenax® obtainable from the company Buchem B.V, poly(2,6-diphenyl-p-phenylene oxide), particle size 60-80 mesh, pore size 200 nm), when the recycled cardboard comprises at least 300-1000 mg/kg mineral oil (sum of MOSH 14-24, MOSH 24-35, MOAH 14-24 and MOAH 24-35) and the proportion of the fraction MOSH 14-24 in the mineral oil is at least 30% by weight. The above migration measurement is taken at 40° C. and for the duration of 10 days.

With the use according to the invention of the coated film in the foodstuffs packaging according to the invention, merely at most 1.6%, in particular at most 1.4%, of the MOSH 24-35 fraction present in the recycled cardboard preferably migrate into a foodstuff simulant pursuant to COMMISSION REGULATION (EC) no. 10/2011 of 14 Jan. 2011 (Tenax® obtainable from the company Buchem B.V, poly(2,6-diphenyl-p-phenylene oxide), particle size 60-80 mesh, pore size 200 nm), when the recycled cardboard comprises at least 300-1000 mg/kg mineral oil (sum of MOSH 14-24, MOSH 24-35, MOAH 14-24 and MOAH 24-35) and the proportion of the fraction MOSH 24-35 in the mineral oil is at least 10% by weight. The above migration measurement is taken at 40° C. and for the duration of 10 days.

With the use according to the invention of the coated film in the foodstuffs packaging according to the invention, merely at most 0.5%, in particular at most 0.3%, of the MOAH 14-24 fraction present in the recycled cardboard preferably migrates into a foodstuff simulant pursuant to COMMISSION REGULATION (EC) no. 10/2011 of 14 Jan. 2011 (Tenax® obtainable from the company Buchem B.V, poly(2,6-diphenyl-p-phenylene oxide), particle size 60-80 mesh, pore size 200 nm), when the recycled cardboard comprises at least 300-1000 mg/kg mineral oil (sum of MOSH 14-24, MOSH 24-35, MOAH 14-24 and MOAH 24-35) and the proportion of the fraction MOAH 14-24 in the mineral oil is at least 10% by weight. The above migration measurement is taken at 40° C. and for the duration of 10 days.

With the use according to the invention of the coated film in the foodstuffs packaging according to the invention, merely at most 3.5%, in particular at most 2.0%, particularly preferably at most 1.0%, of the MOAH 24-35 fraction present in the recycled cardboard preferably migrate into a foodstuff simulant pursuant to COMMISSION REGULATION (EC) no. 10/2011 of 14 Jan. 2011 (Tenax® obtainable from the company Buchem B.V, poly(2,6-diphenyl-p-phenylene oxide), particle size 60-mesh, pore size 200 nm), when the recycled cardboard comprises at least 300-1000 mg/kg mineral oil (sum of MOSH 14-24, MOSH 24-35, MOAH 14-24 and MOAH 24-35) and the proportion of the fraction MOAH 24-35 in the mineral oil is at least 1% by weight. The above migration measurement is taken at 40° C. and for the duration of 10 days.

The present invention also relates to the use of the film described in the introduction for the production of foodstuffs packaging comprising recycled cardboard.

The film contained in the foodstuffs packaging according to the invention is produced by means of extrusion or coextrusion methods known per se, wherein the stenter method is preferred in particular.

To this end, the melts corresponding to the individual layers of the film are coextruded through a flat film die, the film thus obtained is removed for solidification on one or more roll(s), the film is then stretched (oriented), the stretched film is then heat set and optionally plasma-, corona- or flame-treated at the surface layer intended for treatment.

More specifically, as in the extrusion method, the polymers or the polymer mixture of the individual layers is/are compressed here in an extruder and liquefied, wherein optionally added additives may already be contained in the polymer or in the polymer mixture. Alternatively, these additives can also be incorporated via a master batch.

The melts are then optionally pressed jointly and simultaneously through a flat film die (slit die), and the pressed multilayer film is removed on one or more take-off rolls at a temperature from 5 to 100° C., preferably 10 to 50° C., wherein said film cools and solidifies.

The film thus obtained is then stretched longitudinally and transversely to the extrusion direction, which leads to an orientation of the molecule chains. The longitudinal stretching is preferably performed at a temperature from 80 to 150° C., expediently with the aid of two rolls running at different speeds in accordance with the sought draw ratio, and the transverse stretching is preferably performed at a temperature from 120 to 170° C. with the aid of an appropriate clip frame. The longitudinal draw ratios lie in the range from 4 to 8, preferably 4.5 to 6. The transverse draw ratios lie in the range from 5 to 10, preferably 7 to 9.

The stretching of the film is followed by the heat setting of said film (heat treatment), wherein the film is held for approximately 0.1 to 10 s long at a temperature from 100 to 160° C. The film is then usually rolled up using a winding device.

Following the biaxial stretching, one or both surface/s of the film is/are preferably plasma-, corona- or flame-treated in accordance with one of the known methods. The treatment intensity generally lies in the range from 35 to 45 mN/m, preferably 37 to 45 mN/m, in particular 38 to 41 mN/m.

For the alternative corona treatment the film is passed through between two conductor elements serving as electrodes, wherein a sufficiently high voltage, usually an AC voltage (approximately 10,000 V and 10,000 Hz), is applied between the electrodes so that spray or corona discharges can take place. Due to the spray or corona discharge, the air above the film surface is ionised and reacts with the molecules of the film surface, such that polar deposits in the essentially unipolar polymer matrix are produced. The treatment intensities lie within the conventional scope, wherein 37 to 45 mN/m are preferred.

The coextruded multi-layer film is then provided on one or both sides on one or both outer surface(s) with the above-described coatings in accordance with the methods known per se.

To characterise the raw materials and the films, the following measurement methods were used:

Melt Flow Index

The melt flow index was measured in accordance with DIN 53 735 and 21.6 N load and 230° C.

Determination of the Ethylene Content

The ethylene content of the polyolefin copolymers was determined by means of 13C-NMR spectroscopy. The measurements were taken using a nuclear magnetic resonance spectrometer from the company Bruker Avance 360. The copolymer to be characterised was dissolved in tetrachloroethane, such that a 10% mixture was produced. Octamethyltetrasiloxane (OTMS) was added as reference standard. The nuclear magnetic resonance spectrum was measured at 120° C. The spectra were evaluated as described in J.C. Randall Polymer Sequence Distribution (Academic Press, New York, 1977).

Melting Point and Melt Enthalpy

The melting point and the melt enthalpy were determined by means of a DSC (differential scanning calometry) measurement (DIN 51 007 and DIN 53 765). A few milligrams (3 to 5 mg) of the raw material to be characterised were heated in a differential calorimeter with a heating rate of 20° C. per minute. The heat flow rate was plotted against the temperature and the melting point was determined as maximum of the melt curve, and the melt enthalpy was determined as the area of the respective melt peak.

Density

The density was determined in accordance with DIN 53 479, method A.

Surface Tension

The surface tension was determined by means of ink methods in accordance with DIN 53 364.

Friction

The friction was measured in accordance with DIN 533375.

Migration Measurement

The migration of the MOSH and MOAH mineral oils was measured in accordance with the method developed by the BfR (Federal Institute for Risk Assessment) in collaboration with the Kantonalen Labor, Zurich. It was based on an analysis by means of gas chromatography of the mineral oils following manual pre-separation by column chromatography (“determination of hydrocarbons from mineral oil (MOSH and MOAH) or plastics (POAH, PAO) in packaging materials and dry foodstuffs by means of solid phase extraction and GC-FID”). The method was presented at the conference “Mineral oils in Foodstuffs Packaging—Development and Solution Approaches”, which took place on 22 and 23 Sep. 2011 in Berlin. A test substance Tenax® obtainable from the company Buchem B.V (poly(2,6-diphenyl-p-phenylene oxide), particle size 60-80 mesh, pore size 200 nm) was used as foodstuff simulant.

Test structure (FIG. 1): A cardboard saturated with a defined quantity of mineral oil was covered with the sample to be measured, Tenax® was distributed thereon, and the entire assembly was stored in a closed system made of aluminium (temperature 40° C., time 10 days).

Following the storage time, the Tenax® was extracted with hexane and suitable internal standards were added (solid phase extraction), then a separation was performed by means of liquid chromatography (LC) with a stationary phase made of silica gel doped with 0.3% silver nitrate and a mobile phase initially of hexane, then a mixture of hexane, dichloromethane and toluene. The eluate was separated in a third step by means of gas chromatography, and detection was performed in a manner deviating from the above-cited BfR method by means of GC-MS/FID.

The invention will now be explained by the following examples.

Production of the Uncoated Films

The films type 1 to 3 were produced in accordance with the known coextrusion method. Here, a transparent three-layered film with cover layers on either side and with a total thickness of 25 μm was produced by coextrusion and subsequent stepwise orientation in the longitudinal and transverse direction. The cover layers each had a thickness of 0.9 μm.

FILM TYPE 1: Base layer: Approx. 100% by weight isotactic propylene homopolymer with a melting point of 163° C. and a melt flow index of 3.2 g/10 min. Cover layers: Approx. 100% by weight static ethylene-propylene-butylene terpolymer with an ethylene content of 3% by weight and a butylene content of 6% by weight (rest propylene). 0.1% by weight SiO₂ as antiblocking agent with a mean particle size d₅₀ of 5 μm

The production conditions in the individual method steps were:

Extrusion: Temperatures Base layer: 260° C. Cover layers: 240° C. Temperature of the  30° C. take-off roll: Longitudinal Temperature: 120° C. stretching: Longitudinal draw ratio: 5.5 Transverse Temperature: 160° C. stretching: Transverse draw ratio: 9   Fixing: Temperature: 130° C. Convergence 20%

All layers of the film contained neutralising agents and stabilisers in the conventional quantities. Both surfaces were pre-treated by means of corona in order to increase the surface tension.

Film Type 2

A film was produced in accordance with film type 1. In contrast to film type 1, both cover layers contained a static ethylene-propylene copolymer with an ethylene content of approx. 4.5% by weight and a softening point of approx. 130° C.

Film Type 3 Comparative Example

A film was produced in accordance with film type 1. In contrast to film type 1, the base layer additionally contained erucic acid amide as lubricant in a quantity of 0.05% by weight and a bis-ethoxylated amine in a quantity of 0.09% by weight.

Coating

A polyethylene imine adhesion promoter was first applied to the above-described uncoated film and then dried. Different coatings made of acrylate polymer, PVDC or vinyl alcohol polymer were then applied by means of engraving rolls.

EXAMPLE 1

A 1% by weight polyethylene imine dispersion was applied on either side to film type 1 and was dried. An acrylate polymer dispersion from the company NeoResins with trade name BT36 with a solids content of 20% by weight was then applied likewise on either side and was dried. Besides the acrylate polymer dispersion, additives such as Carnauba wax and antiblocking agent were used. The quantity was selected such that sufficient antiblock effect for unwinding the film roll and also a frictional value of approximately 0.3 were achieved.

The thickness of the acrylate polymer layer was 0.8 μm, which corresponded to a coating weight of 0.8 g/m².

EXAMPLE 2

A film as described in Example 1 was produced. In contrast to Example 1, however, only side 1 of film type 1 was coated with the acrylate polymer dispersion. Side 2 was coated on the adhesion promoter layer with a polyvinyl chloride dispersion from the company Solvin with the trade name Diofan A114 having a solids content of 50% by weight. Similarly to Example 1, additives (Carnauba wax and antiblock) were also added here to both sides. The thickness of the polyvinyl chloride layer was 2.0 μm, which corresponded to a coating weight of 3.5 g/m².

EXAMPLE 3

A 1% by weight polyethylene imine dispersion was applied to film type 2 on side 1 and was dried. A vinyl alcohol dispersion from the company Kurary with the trade name Mowiol 3-98 and Exceval AQ-4005 (in the ratio 1:1) having a solids content of, on the whole, 10% by weight was applied thereto and dried.

The thickness of the coating layer was 0.8 μm, which corresponded to a coating weight of 0.8 g/m². In addition, additives such as Carnauba wax and antiblocking agent were used. The quantity was selected such that sufficient antiblock effect for unwinding the film roll and also a frictional value of approximately 0.3 were achieved.

EXAMPLE 4

A film was produced in accordance with Example 3. In contrast to Example 3, a 1% by weight polyethylene imine dispersion was additionally applied to side 2 and was dried. An acrylate polymer dispersion from the company NeoResins with the trade name BT36, having a solids content of 20% by weight was applied to this adhesion promoter layer and dried. Besides the acrylate polymer dispersion, additives such as Carnauba wax and antiblocking agent were used. The quantity was selected such that sufficient antiblock effect for unwinding the film roll and also a frictional value of approximately 0.3 were achieved. The thickness of the acrylate polymer layer was 0.8 μm, which corresponded to a coating weight of 0.8 g/m².

Comparative Example

Film type 3 was used without coating.

The above coating was varied in accordance with the invention and is summarised in Table 1:

Coating Mineral oil barrier Front side = +++ very good side 1 Coating ++ good (facing towards Rear side = + satisfactory the cardboard) side 2 − no barrier Example 1 Acrylate polymer Acrylate polymer MOSH 14-24 +++ (film type 1: 0.8 μm coating 0.8 μm coating MOSH 24-35 ++ terpo-homo- layer thickness layer thickness MOAH 14-24 +++ terpo) MOAH 24-35 +++ Example 2 Acrylate polymer PVDC MOSH 14-24 ++ (film type 1: 0.8 μm coating 2.0 μm coating MOSH 24-35 ++ terpo-homo- layer thickness layer thickness MOAH 14-24 +++ terpo) MOAH 24-35 +++ Example 3 Vinyl alcohol none MOSH 14-24 ++ (film type 2: polymer (EVOH) MOSH 24-35 + Copo-homo- 0.8 μm coating MOAH 14-24 +++ Copo) layer thickness MOAH 24-35 +/− Example 4 Vinyl alcohol Acrylate polymer MOSH 14-24 +++ (film type 2: polymer (EVOH) 0.8 μm coating MOSH 24-35 ++ Copo-homo- 0.8 μm coating layer thickness MOAH 14-24 +++ Copo) layer thickness MOAH 24-35 ++ Comparative none none MOSH 14-24 − example 1 MOSH 24-35 − (film type 3) MOAH 14-24 − MOAH 24-35 − 

1.-24. (canceled)
 25. A foodstuff packaging comprising: a) a foodstuff, b) a polyolefin-based film which film encases the foodstuff, c) a cardboard based on recycled cardboard, which encases the polyolefin-based film, in particular the film based on biaxially oriented polypropylene (boPP) films, containing the foodstuff, wherein the polyolefin-based film comprises at least one coating comprising (i) acrylate polymer and/or (ii) halogen-containing vinyl polymers and/or vinylidene polymers and/or (iii) polymers based on vinyl alcohol (VOH), and the coating is present at least on the side of the film facing towards the cardboard based on recycled cardboard.
 26. The foodstuff packaging according to claim 25, wherein the film and/or the cardboard does not have any metallization preventing the migration of mineral oils into the packaged foodstuff).
 27. The foodstuff packaging according to claim 25, wherein the film is monolayered or multi-layered and comprises a base layer containing at least 70% by weight of the polyolefin in relation to the weight of the layer.
 28. The foodstuff packaging according to claim 27, wherein the polyolefin-based film is a film based on biaxially oriented polypropylene (boPP) films and the base layer contains 85 to 95% by weight, of the polyolefin, in each case in relation to the weight of the layer.
 29. The foodstuff packaging according to claim 28, wherein the film is monolayered and contains 90 to 100% by weight, of propylene polymers of which the melting point is 120° C. and which have a melt flow index from 1 to 10 g/10 min at 230° C. and a force of 21.6 N (DIN 53735).
 30. The foodstuff packaging according to claim 25, wherein the propylene polymer is a mixture of propylene homopolymers and/or copolymers and/or terpolymers and other polyolefins wherein the mixture contains at least 50% by weight of propylene polymer.
 31. The foodstuff packaging according claim 25, wherein the polyolefin film contains pigments in a quantity from 0.5 to 10% by weight.
 32. The foodstuff packaging according to claim 25, wherein the polyolefin-based film has a thickness from 20 to 100 μm.
 33. The foodstuff packaging according to claim 25, wherein the polyolefin-based film comprises, on one or both sides, an adhesion promoter made of polyethylene imine, to which the coating/s is/are applied.
 34. The foodstuff packaging according to claim 34, wherein the coating is present on both sides of the film.
 35. The foodstuff packaging according to claim 25, wherein the coating of the film on each side has in each case a total thickness between 0.4-5 μm.
 36. The foodstuff packaging according to claim 35, wherein the coating is multi-layered and, with a coating made of halogen-containing vinyl polymers and/or vinylidene polymers, initially has a secondary primer layer based on vinyl acetate/acrylate, and the layer thickness of the secondary primer layer comprises 50-100% of the layer thickness of the coating made of halogen-containing vinyl polymers and/or vinylidene polymers.
 37. The foodstuff packaging according to claim 25, wherein acrylate is an acrylate homopolymer and/or acrylate copolymer based on alkyl acrylates.
 38. The foodstuff packaging according to claim 25, wherein the halogen-containing vinyl polymer and/or vinylidene polymer is based on vinyl chloride and/or is vinyl chloride, which preferably comprises a copolymer based on vinyl acetate or acrylate.
 39. The foodstuff packaging according to claim 25, wherein the coating material made of a polymer based on vinyl alcohol (VOH) comprises a mixture of ethylene vinyl alcohol (EVOH) and polyvinyl alcohol, and said mixture comprising 5-15% by weight of a mixture of ethylene vinyl alcohol and polyvinyl alcohol, in the ratio 0.8-1.2 to 1.2-0.8 (ratios by weight).
 40. The foodstuff packaging according to claim 25, wherein the quantity of coating per side of the film (after drying) is between 0.5 and 1.0 g/m² for coating materials made of polymers based on vinyl alcohol (VOH), and the layer thickness is 1 to 1.5 μm (±0.2 μm).
 41. The foodstuff packaging according to claim 25, wherein the quantity of coating per side of the film after drying is between 0.5 and 1.5 g/m² for coating materials based on acrylate, and the layer thickness is 1 to 1.5 μm.
 42. The foodstuff packaging according to claim 25, wherein the quantity of coating per side of the film after drying is between 2.5 and 4 g/m² for coating materials based on halogen-containing vinyl polymers and/or vinylidene polymers, wherein the above quantity includes the secondary primer layer based on vinyl acetate/acrylate, and the layer thickness is 1.5 to 2.0 μm (±0.2 μm).
 43. The foodstuff packaging according to claim 25, wherein the recycled cardboard contains at least 300-1000 mg/kg mineral oil.
 44. The foodstuff packaging according to claim 25, wherein the film comprises a barrier for the mineral oils present in the recycled cardboard and at most 1%, of the MOSH 14-24 fraction present in the recycled cardboard diffuses into a foodstuff′ simulant when the proportion of the fraction MOSH 14-24 in the mineral oil of the recycled cardboard is at least 30% by weight.
 45. The foodstuff packaging according to claim 25, wherein the film comprises a barrier for the mineral oils present in the recycled cardboard and at most 1.6% of the MOSH 24-35 fraction present in the recycled cardboard diffuse into a foodstuff simulant when the proportion of the fraction MOSH 24-35 in the mineral oil of the recycled cardboard is at least 10% by weight.
 46. The foodstuff packaging according to claim 25, wherein the film comprises a barrier for the mineral oils present in the recycled cardboard and at most 0.5% of the MOAH 14-24 fraction present in the recycled cardboard diffuses into as foodstuff simulant when the proportion of the fraction MOAH 14-24 in the mineral oil of the recycled cardboard is at least 10% by weight.
 47. The foodstuff packaging according to claim 25, wherein the film comprises a barrier for the mineral oils present in the recycled cardboard and at most 3.5%, of the MOAH 24-35 fraction present in the recycled cardboard diffuse into a foodstuff simulant when the proportion of the fraction MOAH 24-35 in the mineral oil of the recycled cardboard is at least 1% by weight.
 48. The foodstuff packaging according to claim 25, wherein the foodstuffs packaging consists of the cardboard and the film and does not comprise any further metal layer. 